Exercise step



FIG. 1 is a front elevation view of an exercise step showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is an end elevation view thereof with the opposite end being identical;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a rear elevation view thereof; and,

FIG. 6 is a perspective view thereof. 

The ornamental design for an exercise step, as shown and described. 